Prior Art
Thermally insulating materials such as foamed plastics, glass wool or rock wool have been applied to the outside or inside of buildings, and after such application these insulating materials have been covered with surface materials. Because such insulating materials are weak, heavy decorative products such as tile cannot be used to cover the insulating materials, necessitating the use of light-weight surface materials which are less decorative.
Attempts have been made to use decorative thermally insulating foam glass tile as the outside covering material of buildings. Such conventional foam glass pieces have poor strength, especially surface strength, and are therefore not practical. The poor strength of these pieces may be increased by applying a strong glaze layer 100 on such a foam glass body 102 as shown in FIG. 5.
The glazed foam glass pieces 104 which result, however, have serious disadvantages as summarized below:
1. The glazed layer needs to be thick to prevent it from developing cracks, pinholes and unevenness as the glaze is elongated in all directions when the foam glass body is expanded during the course of production.
2. The step of forming such thick glaze layers is troublesome and complicated. Although thick glaze coating is carried out more easily when powder glaze materials are used rather than wet glaze materials, there are still drawbacks such as, for instance, the need for complicated application apparatus, the likelihood that the glazed layer will peel off and the difficulty in applying the glaze onto complicated surfaces.
3. The glaze layer 100 is likely to shrink while the foam glass body 104 expands during the course of firing, thereby causing deformation of the foam glass pieces, such as by warping, and a decrease in the strength of the glazed layer due to stress.
4. Since the glaze layer has good thermal conductivity and is comparatively heavy, the thick glaze layer decreases the thermal insulating capability of the foam piece and increases the weight thereof.
5. Foam glass pieces having a thick glaze layer have very poor thermal shock resistance when subjected to a sudden change in temperature because the glaze layer and foam glass body have significantly different heat capacities and thermal conductivities.
6. It is difficult to apply a thick glaze layer onto a foam glass body having complicated surface structures.